I have been using bulletproof for a month now. I apply it twice a week; change my nail color about every week or so. I've always had weak nails that break easily. My nails are now strong and gorgeous. Tried the gel stuff, HATE IT; leaves your nails very weak. Highly recommend this product. For less than $5, you can't go wrong; beats nail salon prices!
Regardless of what the instructions say, do not use this as a top coat over colored nail polish. It will completely dissolve the color while you are brushing it on. I have not used as a base coat, but I can't imagine you would fare much better.